A complexometric method for the determination of mercury(II) in presence of other metal ions is described based on the selective masking action of 1-propane thiol towards mercury(H). Mercury(II) present in a given sample solution is first complexed with an excess of EDTA and the unreacted EDTA is titrated against lead nitrate solution at pH 5-6 (hexamine buffer) using xylenol orange as the indicator. A 0.8% aqueous solution of 1-propane thiol is then added to displace EDTA from the Hg(II)EDTA complex. The released EDTA is titrated with standard lead nitrate solution as before. Reproducible and accurate results are obtained for 4-85 mg of mercury(II), with relative error less than +/- 0.23 % and coefficient of variation not more than +/- 0.41 %. The effects of various ions were studied. The method is used for the analysis of mercury(II) in its synthetic alloy mixtures and also in complexes.